1. Field of the Disclosure
Embodiments disclosed herein relate generally to joining subsea stack assemblies. In particular, embodiments disclosed herein relate to methods to design and assemble interchangeable subsea stack assemblies.
2. Background Art
Well control is an important aspect of oil and gas exploration. When drilling a well in, for example, oil and gas exploration applications, devices must be put in place to prevent injury to personnel and equipment associated with the drilling activities. One such well control device is known as a blowout preventer (BOP).
Blowout preventers are generally used to seal a wellbore. For example, drilling wells in oil or gas exploration involves penetrating a variety of subsurface geologic structures, or “layers.” Each layer generally comprises a specific geologic composition such as, for example, shale, sandstone, limestone, etc. Each layer may contain trapped fluids or gas at different formation pressures, and the formation pressures increase with increasing depth. The pressure in the wellbore is generally adjusted to at least balance the formation pressure by, for example, increasing a density of drilling mud in the wellbore or increasing pump pressure at the surface of the well.
There are occasions during drilling operations when a wellbore may penetrate a layer having a formation pressure substantially higher than the pressure maintained in the wellbore. When this occurs, the well is said to have “taken a kick.” The pressure increase associated with the kick is generally produced by an influx of formation fluids (which may be a liquid, a gas, or a combination thereof) into the wellbore. The relatively high pressure kick tends to propagate from a point of entry in the wellbore uphole (from a high pressure region to a low pressure region). If the kick is allowed to reach the surface, drilling fluid, well tools, and other drilling structures may be blown out of the wellbore. These “blowouts” often result in catastrophic destruction of the drilling equipment (including, for example, the drilling rig) and in substantial injury or death of rig personnel.
Because of the risk of blowouts, blowout preventers are typically installed at the surface or on the sea floor in deep water drilling arrangements so that kicks may be adequately controlled and “circulated out” of the system. Blowout preventers may be activated to effectively seal in a wellbore until active measures can be taken to control the kick. There are several types of blowout preventers, the most common of which are annular blowout preventers and ram-type blowout preventers.
Annular blowout preventers typically comprise annular elastomer “packers” that may be activated (e.g., inflated) to encapsulate drill pipe and well tools and completely seal the wellbore. A second type of the blowout preventer is the ram-type blowout preventer. Ram-type preventers typically comprise a body and at least two oppositely disposed bonnets. The bonnets are generally secured to the body about their circumference with, for example, bolts. Alternatively, bonnets may be secured to the body with a binge and bolts so that the bonnet may be rotated to the side for maintenance access.
Interior of each bonnet contains a piston actuated ram. The functionality of the rams may include pipe rams, shear rams, or blind rams. Pipe rams (including variable bore rams) engage and seal around the drill pipe or well tool left in the wellbore, leaving the engaged objects intact. In contrast, shear rams engage and physically shear the drill pipe or well tools left in the wellbore. Similarly, blind rams engage each other and seal off the wellbore when no drill pipe or well tools are in the wellbore. The rams are typically located opposite of each other and, whether pipe rams, shear rams, or blind rams, the rams typically seal against one another proximate a center of the wellbore in order to seal the wellbore.
As such, many oil and gas bearing formations lie beneath large bodies of water. Producing wells extending into these formations are equipped with subsea wellheads and other underwater installations which rest at the ocean or sea floor. As such, it is customary to provide blowout protection and other related functions during subsea drilling operations. As such subsea blowout preventer installations may be equipped with numerous and varied types of valves, rams, and other operating controls that may be hydraulically, electro-mechanically, or electro-hydraulically operated to control wellbore fluids.
In shallow water, many subsea blowout preventer and flow control installations are controlled hydraulically. These all-hydraulic systems may include a bundle of hydraulic hoses and control lines extending between the surface and subsea facilities. Alternatively, individual hoses may supply hydraulic power from the surface to the subsea installation to monitor the status of the subsea equipment and perform control operations. Advantageously, these systems are simple, reliable, and inexpensive for relatively short hose lengths (i.e., water depths) although response time may be slow. However, in deep-water installations, the response time for a hydraulic system increases and its reliability decreases.
In response to the demands of deep-water subsea environments, electro-hydraulic systems were introduced to improve the performance of traditional hydraulic systems in deep water or over long distances. As such, an electro-hydraulic subsea control cable may employ a multiplex (MUX) hose in which several hydraulic control signals may be multiplexed (e.g., through digital time division) and transmitted. The multitude of signals may then be separated out at the end of the multiplex hose and used to manipulate valves in a control pod of a blowout preventer or another subsea component. While a multiplex umbilical line may be a hydraulic hose, it should be understood that an electrical line may also serve as a multiplexing conduit.
Blowout preventer stacks are typically custom fit during an initial assembly process, which requires the stack assemblies to be test fit together at the surface prior to installation subsea. Further, the current method of manufacture may produce assemblies requiring a custom fit which are not interchangeable. For example, many feed-thrus or interconnects, such as the hydraulic feed-thrus and/or electro-hydraulic cables, between a Lower Marine Riser Package (“LMRP”) and a Lower Stack, require adjustability upon assembly.
Accordingly, there exists a need for a stack assembly having complete interchangeability between an LMRP assembly and any Lower Stack assembly of the same design, without the need for any manual adjustments on the surface.